1. Field of the Invention
The invention relates in general to a signal transmission assembly and a display device applied with the same, and more particularly to a signal transmission assembly capable of enhancing overflowing adhesive uniformity and increasing the bonding intensity, and a display device applied with the same.
2. Description of the Related Art
In a module process of a liquid crystal display, a display panel and a PCB (Print Circuit Board) are connected to each other through a FPC (Flexible Print Circuit) or a TCP/TAB (Tape Carrier Package/Tape Automated Bonding) to achieve the object of transmitting signals. In order to slim the display, the newest COF (Chip On Film) technology reduces the peripheral area of the panel, which is required during the bonding process, such that the display can be applied to a notebook computer, which has to be made slim and light. Although the package methods are different from one another, most of the lead electrode portions of the film substrates are electrically connected to metal conductive bonding pads at one end of the display panel (or one end of the PCB) through an ACF (Anisotropic Conduction Film) after being hot-pressed.
FIG. 1 is a schematic illustration showing a display device in which a PCB is connected to a display panel through a FPC. Referring to FIG. 1, the display panel includes a display area 1 and a non-display area 2. The display panel includes a first substrate 11 having a first electrode 13 formed thereon. The first electrode 13 is located in the non-display area 2 and electrically connected to the display area 1. The display panel also has a second substrate 21, such as a FPC, for connecting the first substrate 11 of the display panel to a third substrate 31, such as a PCB, in order to transmit signals. The first electrode 13 is the conventional metal conductive bonding pad and may be formed by a metal layer on the first substrate 11 and an ITO (Indium Tin Oxide) layer on the metal layer.
As shown in FIG. 1, two ends of the second substrate 21 respectively have a second electrode 22 and a third electrode 23, which pertain to the conventional leads. In addition, conductive layers, such as a first ACF 41 and a second ACF 42, are disposed between the first electrode 13 and the second electrode 22, and between the third electrode 23 and the third substrate 31. The ACF mainly includes an adhesive and numerous conductive particles distributed in the adhesive. After being hot-pressed in the direction as indicated by the arrow, two ends of the second substrate 21 may be electrically connected to the first substrate 11 and the third substrate 31, respectively, so that the signals can be transmitted to the display area 1 of the panel to control the display.
FIGS. 2A and 2B are schematic illustrations showing an ACF being hot-pressed in a conventional method of aligning leads with bonding pads. As shown in FIGS. 2A, 2B and 1, conductive particles 413 distributed in an adhesive 411 of the first ACF 41 can be resin balls serving as cores covered by a conductive metal material such as gold and nickel. After the second substrate 21 and the first substrate 11 are hot-pressed, the second electrode (i.e., the conventional lead) 22 and the first electrode (i.e., the conventional bonding pad) 13 may be electrically connected to each other through the conductive particles 413.
As shown in FIG. 2B, the conventional leads and the bonding pads are aligned with and bonded to each other in a one-to-one manner. When the ACF having the adhesive is hot-pressed, a good adhesive overflowing path is required to prevent the cured adhesive on the bonding surface from having the bonding defect of the non-uniform thickness due to the poor overflowing adhesive. FIG. 3 is a schematic illustration showing a main adhesive overflowing path of the adhesive in the conventional method of aligning the leads with the bonding pads. In the conventional method of aligning the leads with the bonding pads, the adhesive overflows into spacing between two adjacent leads (second electrodes 22) and two adjacent bonding pads (first electrodes 13), and the adhesive overflowing path is indicated by the arrows of FIG. 3. The conventional aligning design is practicable for the leads (bonding pads) having the smaller widths. However, the poor overflowing adhesive becomes a serious problem when the conventional aligning design is used in the leads (bonding pads) having larger widths because the leads and the bonding pads are bonded over a large area and the adhesive closer to the center of the contact surface cannot flow out easily.
FIG. 4 is a schematic illustration showing the poor overflowing adhesive produced using the conventional method to align bonding leads with bonding pads over a large area. As shown in FIG. 4, the areas of the lead and the bonding pad are large, the poor overflowing adhesive 411 after being hot-pressed electrically connects the second substrate 21 to the first substrate 11 only through the conductive particles 413′ close to the outer sides of the lead (second electrode 22) and the bonding pad (first electrode 13) to achieve the object of electrical connection. Thus, the problem of poor electrical connection may be caused. Furthermore, the redundant adhesive 411 after reaction and curing between the lead and the bonding pad results in poor bonding intensity between the lead (second electrode 22) and the bonding pad (first electrode 13), and the repeated twitching or bending during the module assembly process may peel off the lead (second electrode 22) and the bonding pad (first electrode 13).